The spectrum of activity of macrolides, including erythromycin, covers most relevant bacterial species responsible for upper and lower respiratory tract infections. 14-membered ring macrolides are well known for their overall efficacy, safety and lack of serious side effects. Erythromycin, however, is quickly degraded into inactive products in the acidic medium of the stomach resulting in low bioavailability and gastrointestinal side effects. Improvement of erythromycin pharmacokinetics has been achieved through the synthesis of more acid-stable derivatives, for example, roxithromycin, clarithromycin, and the 15-membered ring macrolide azithromycin. However, all of these drugs, including 16-membered ring macrolides, present several drawbacks. They are inactive against MLSB-resistant streptococci (MLSB=Macrolides-Lincosamides-type B Streptogramines) and with the exception of azithromycin, weakly active against Haemophilus influenzae. Furthermore, the resistance of Streptococcus pneumoniae to erythromycin has increased significantly in recent years (5% to above 40%). There is high percentage of cross-resistance to penicillin among these isolates, with a worldwide epidemic spread of 10-40% in some areas.
Kashimura et al. have disclosed 6-O-methylerythromycin derivatives having a tricyclic basic nuclear structure in European Application 559896, published in Nov. 11, 1991. Also, Asaka et al. have disclosed 5-O-desoaminylerythronolide derivatives containing a tricyclic carbamate structure in PCT Application WO 93/21200, published Apr. 22, 1992.
Erythromycin derivatives containing a variety of substituents at the 6-O position have been disclosed in U.S. Pat. Nos. 5,866,549 and 6,075,011 as well as PCT Application WO 00/78773. Furthermore, Ma et al. have described erythromycin derivatives with aryl groups tethered to the C-6 position (Ma et al., J. Med Chem., 44, pp 4137-4156 (2001)). PCT application WO 97/10251, published Mar. 20, 1997, discloses intermediates useful for preparation of 6-O-methyl 3-descladinose erythromycin derivatives. U.S. Pat. Nos. 5,866,549, 6,075,011, 6,878,691, 7,064,100 and PCT application WO 00/78773, published Dec. 28, 2000, also disclose certain 6-O-substituted erythromycin derivatives.